1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Functions related to io context handling 4 */ 5 #include <linux/kernel.h> 6 #include <linux/module.h> 7 #include <linux/init.h> 8 #include <linux/bio.h> 9 #include <linux/blkdev.h> 10 #include <linux/slab.h> 11 #include <linux/sched/task.h> 12 13 #include "blk.h" 14 15 /* 16 * For io context allocations 17 */ 18 static struct kmem_cache *iocontext_cachep; 19 20 /** 21 * get_io_context - increment reference count to io_context 22 * @ioc: io_context to get 23 * 24 * Increment reference count to @ioc. 25 */ 26 void get_io_context(struct io_context *ioc) 27 { 28 BUG_ON(atomic_long_read(&ioc->refcount) <= 0); 29 atomic_long_inc(&ioc->refcount); 30 } 31 EXPORT_SYMBOL(get_io_context); 32 33 static void icq_free_icq_rcu(struct rcu_head *head) 34 { 35 struct io_cq *icq = container_of(head, struct io_cq, __rcu_head); 36 37 kmem_cache_free(icq->__rcu_icq_cache, icq); 38 } 39 40 /* 41 * Exit an icq. Called with ioc locked for blk-mq, and with both ioc 42 * and queue locked for legacy. 43 */ 44 static void ioc_exit_icq(struct io_cq *icq) 45 { 46 struct elevator_type *et = icq->q->elevator->type; 47 48 if (icq->flags & ICQ_EXITED) 49 return; 50 51 if (et->uses_mq && et->ops.mq.exit_icq) 52 et->ops.mq.exit_icq(icq); 53 else if (!et->uses_mq && et->ops.sq.elevator_exit_icq_fn) 54 et->ops.sq.elevator_exit_icq_fn(icq); 55 56 icq->flags |= ICQ_EXITED; 57 } 58 59 /* 60 * Release an icq. Called with ioc locked for blk-mq, and with both ioc 61 * and queue locked for legacy. 62 */ 63 static void ioc_destroy_icq(struct io_cq *icq) 64 { 65 struct io_context *ioc = icq->ioc; 66 struct request_queue *q = icq->q; 67 struct elevator_type *et = q->elevator->type; 68 69 lockdep_assert_held(&ioc->lock); 70 71 radix_tree_delete(&ioc->icq_tree, icq->q->id); 72 hlist_del_init(&icq->ioc_node); 73 list_del_init(&icq->q_node); 74 75 /* 76 * Both setting lookup hint to and clearing it from @icq are done 77 * under queue_lock. If it's not pointing to @icq now, it never 78 * will. Hint assignment itself can race safely. 79 */ 80 if (rcu_access_pointer(ioc->icq_hint) == icq) 81 rcu_assign_pointer(ioc->icq_hint, NULL); 82 83 ioc_exit_icq(icq); 84 85 /* 86 * @icq->q might have gone away by the time RCU callback runs 87 * making it impossible to determine icq_cache. Record it in @icq. 88 */ 89 icq->__rcu_icq_cache = et->icq_cache; 90 call_rcu(&icq->__rcu_head, icq_free_icq_rcu); 91 } 92 93 /* 94 * Slow path for ioc release in put_io_context(). Performs double-lock 95 * dancing to unlink all icq's and then frees ioc. 96 */ 97 static void ioc_release_fn(struct work_struct *work) 98 { 99 struct io_context *ioc = container_of(work, struct io_context, 100 release_work); 101 unsigned long flags; 102 103 /* 104 * Exiting icq may call into put_io_context() through elevator 105 * which will trigger lockdep warning. The ioc's are guaranteed to 106 * be different, use a different locking subclass here. Use 107 * irqsave variant as there's no spin_lock_irq_nested(). 108 */ 109 spin_lock_irqsave_nested(&ioc->lock, flags, 1); 110 111 while (!hlist_empty(&ioc->icq_list)) { 112 struct io_cq *icq = hlist_entry(ioc->icq_list.first, 113 struct io_cq, ioc_node); 114 struct request_queue *q = icq->q; 115 116 if (spin_trylock(q->queue_lock)) { 117 ioc_destroy_icq(icq); 118 spin_unlock(q->queue_lock); 119 } else { 120 spin_unlock_irqrestore(&ioc->lock, flags); 121 cpu_relax(); 122 spin_lock_irqsave_nested(&ioc->lock, flags, 1); 123 } 124 } 125 126 spin_unlock_irqrestore(&ioc->lock, flags); 127 128 kmem_cache_free(iocontext_cachep, ioc); 129 } 130 131 /** 132 * put_io_context - put a reference of io_context 133 * @ioc: io_context to put 134 * 135 * Decrement reference count of @ioc and release it if the count reaches 136 * zero. 137 */ 138 void put_io_context(struct io_context *ioc) 139 { 140 unsigned long flags; 141 bool free_ioc = false; 142 143 if (ioc == NULL) 144 return; 145 146 BUG_ON(atomic_long_read(&ioc->refcount) <= 0); 147 148 /* 149 * Releasing ioc requires reverse order double locking and we may 150 * already be holding a queue_lock. Do it asynchronously from wq. 151 */ 152 if (atomic_long_dec_and_test(&ioc->refcount)) { 153 spin_lock_irqsave(&ioc->lock, flags); 154 if (!hlist_empty(&ioc->icq_list)) 155 queue_work(system_power_efficient_wq, 156 &ioc->release_work); 157 else 158 free_ioc = true; 159 spin_unlock_irqrestore(&ioc->lock, flags); 160 } 161 162 if (free_ioc) 163 kmem_cache_free(iocontext_cachep, ioc); 164 } 165 EXPORT_SYMBOL(put_io_context); 166 167 /** 168 * put_io_context_active - put active reference on ioc 169 * @ioc: ioc of interest 170 * 171 * Undo get_io_context_active(). If active reference reaches zero after 172 * put, @ioc can never issue further IOs and ioscheds are notified. 173 */ 174 void put_io_context_active(struct io_context *ioc) 175 { 176 struct elevator_type *et; 177 unsigned long flags; 178 struct io_cq *icq; 179 180 if (!atomic_dec_and_test(&ioc->active_ref)) { 181 put_io_context(ioc); 182 return; 183 } 184 185 /* 186 * Need ioc lock to walk icq_list and q lock to exit icq. Perform 187 * reverse double locking. Read comment in ioc_release_fn() for 188 * explanation on the nested locking annotation. 189 */ 190 retry: 191 spin_lock_irqsave_nested(&ioc->lock, flags, 1); 192 hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) { 193 if (icq->flags & ICQ_EXITED) 194 continue; 195 196 et = icq->q->elevator->type; 197 if (et->uses_mq) { 198 ioc_exit_icq(icq); 199 } else { 200 if (spin_trylock(icq->q->queue_lock)) { 201 ioc_exit_icq(icq); 202 spin_unlock(icq->q->queue_lock); 203 } else { 204 spin_unlock_irqrestore(&ioc->lock, flags); 205 cpu_relax(); 206 goto retry; 207 } 208 } 209 } 210 spin_unlock_irqrestore(&ioc->lock, flags); 211 212 put_io_context(ioc); 213 } 214 215 /* Called by the exiting task */ 216 void exit_io_context(struct task_struct *task) 217 { 218 struct io_context *ioc; 219 220 task_lock(task); 221 ioc = task->io_context; 222 task->io_context = NULL; 223 task_unlock(task); 224 225 atomic_dec(&ioc->nr_tasks); 226 put_io_context_active(ioc); 227 } 228 229 static void __ioc_clear_queue(struct list_head *icq_list) 230 { 231 unsigned long flags; 232 233 while (!list_empty(icq_list)) { 234 struct io_cq *icq = list_entry(icq_list->next, 235 struct io_cq, q_node); 236 struct io_context *ioc = icq->ioc; 237 238 spin_lock_irqsave(&ioc->lock, flags); 239 ioc_destroy_icq(icq); 240 spin_unlock_irqrestore(&ioc->lock, flags); 241 } 242 } 243 244 /** 245 * ioc_clear_queue - break any ioc association with the specified queue 246 * @q: request_queue being cleared 247 * 248 * Walk @q->icq_list and exit all io_cq's. 249 */ 250 void ioc_clear_queue(struct request_queue *q) 251 { 252 LIST_HEAD(icq_list); 253 254 spin_lock_irq(q->queue_lock); 255 list_splice_init(&q->icq_list, &icq_list); 256 257 if (q->mq_ops) { 258 spin_unlock_irq(q->queue_lock); 259 __ioc_clear_queue(&icq_list); 260 } else { 261 __ioc_clear_queue(&icq_list); 262 spin_unlock_irq(q->queue_lock); 263 } 264 } 265 266 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node) 267 { 268 struct io_context *ioc; 269 int ret; 270 271 ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO, 272 node); 273 if (unlikely(!ioc)) 274 return -ENOMEM; 275 276 /* initialize */ 277 atomic_long_set(&ioc->refcount, 1); 278 atomic_set(&ioc->nr_tasks, 1); 279 atomic_set(&ioc->active_ref, 1); 280 spin_lock_init(&ioc->lock); 281 INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH); 282 INIT_HLIST_HEAD(&ioc->icq_list); 283 INIT_WORK(&ioc->release_work, ioc_release_fn); 284 285 /* 286 * Try to install. ioc shouldn't be installed if someone else 287 * already did or @task, which isn't %current, is exiting. Note 288 * that we need to allow ioc creation on exiting %current as exit 289 * path may issue IOs from e.g. exit_files(). The exit path is 290 * responsible for not issuing IO after exit_io_context(). 291 */ 292 task_lock(task); 293 if (!task->io_context && 294 (task == current || !(task->flags & PF_EXITING))) 295 task->io_context = ioc; 296 else 297 kmem_cache_free(iocontext_cachep, ioc); 298 299 ret = task->io_context ? 0 : -EBUSY; 300 301 task_unlock(task); 302 303 return ret; 304 } 305 306 /** 307 * get_task_io_context - get io_context of a task 308 * @task: task of interest 309 * @gfp_flags: allocation flags, used if allocation is necessary 310 * @node: allocation node, used if allocation is necessary 311 * 312 * Return io_context of @task. If it doesn't exist, it is created with 313 * @gfp_flags and @node. The returned io_context has its reference count 314 * incremented. 315 * 316 * This function always goes through task_lock() and it's better to use 317 * %current->io_context + get_io_context() for %current. 318 */ 319 struct io_context *get_task_io_context(struct task_struct *task, 320 gfp_t gfp_flags, int node) 321 { 322 struct io_context *ioc; 323 324 might_sleep_if(gfpflags_allow_blocking(gfp_flags)); 325 326 do { 327 task_lock(task); 328 ioc = task->io_context; 329 if (likely(ioc)) { 330 get_io_context(ioc); 331 task_unlock(task); 332 return ioc; 333 } 334 task_unlock(task); 335 } while (!create_task_io_context(task, gfp_flags, node)); 336 337 return NULL; 338 } 339 EXPORT_SYMBOL(get_task_io_context); 340 341 /** 342 * ioc_lookup_icq - lookup io_cq from ioc 343 * @ioc: the associated io_context 344 * @q: the associated request_queue 345 * 346 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called 347 * with @q->queue_lock held. 348 */ 349 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q) 350 { 351 struct io_cq *icq; 352 353 lockdep_assert_held(q->queue_lock); 354 355 /* 356 * icq's are indexed from @ioc using radix tree and hint pointer, 357 * both of which are protected with RCU. All removals are done 358 * holding both q and ioc locks, and we're holding q lock - if we 359 * find a icq which points to us, it's guaranteed to be valid. 360 */ 361 rcu_read_lock(); 362 icq = rcu_dereference(ioc->icq_hint); 363 if (icq && icq->q == q) 364 goto out; 365 366 icq = radix_tree_lookup(&ioc->icq_tree, q->id); 367 if (icq && icq->q == q) 368 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */ 369 else 370 icq = NULL; 371 out: 372 rcu_read_unlock(); 373 return icq; 374 } 375 EXPORT_SYMBOL(ioc_lookup_icq); 376 377 /** 378 * ioc_create_icq - create and link io_cq 379 * @ioc: io_context of interest 380 * @q: request_queue of interest 381 * @gfp_mask: allocation mask 382 * 383 * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they 384 * will be created using @gfp_mask. 385 * 386 * The caller is responsible for ensuring @ioc won't go away and @q is 387 * alive and will stay alive until this function returns. 388 */ 389 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q, 390 gfp_t gfp_mask) 391 { 392 struct elevator_type *et = q->elevator->type; 393 struct io_cq *icq; 394 395 /* allocate stuff */ 396 icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO, 397 q->node); 398 if (!icq) 399 return NULL; 400 401 if (radix_tree_maybe_preload(gfp_mask) < 0) { 402 kmem_cache_free(et->icq_cache, icq); 403 return NULL; 404 } 405 406 icq->ioc = ioc; 407 icq->q = q; 408 INIT_LIST_HEAD(&icq->q_node); 409 INIT_HLIST_NODE(&icq->ioc_node); 410 411 /* lock both q and ioc and try to link @icq */ 412 spin_lock_irq(q->queue_lock); 413 spin_lock(&ioc->lock); 414 415 if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) { 416 hlist_add_head(&icq->ioc_node, &ioc->icq_list); 417 list_add(&icq->q_node, &q->icq_list); 418 if (et->uses_mq && et->ops.mq.init_icq) 419 et->ops.mq.init_icq(icq); 420 else if (!et->uses_mq && et->ops.sq.elevator_init_icq_fn) 421 et->ops.sq.elevator_init_icq_fn(icq); 422 } else { 423 kmem_cache_free(et->icq_cache, icq); 424 icq = ioc_lookup_icq(ioc, q); 425 if (!icq) 426 printk(KERN_ERR "cfq: icq link failed!\n"); 427 } 428 429 spin_unlock(&ioc->lock); 430 spin_unlock_irq(q->queue_lock); 431 radix_tree_preload_end(); 432 return icq; 433 } 434 435 static int __init blk_ioc_init(void) 436 { 437 iocontext_cachep = kmem_cache_create("blkdev_ioc", 438 sizeof(struct io_context), 0, SLAB_PANIC, NULL); 439 return 0; 440 } 441 subsys_initcall(blk_ioc_init); 442